theorem
  for V being RealLinearSpace, W being Subspace of V, L being
Linear_Compl of W, v being VECTOR of V, t being Element of [:the carrier of V,
the carrier of V:] holds t`1 + t`2 = v & t`1 in W & t`2 in L implies t = v |--
  (W,L)
proof
  let V be RealLinearSpace, W be Subspace of V, L be Linear_Compl of W;
  V is_the_direct_sum_of W,L by Th35;
  hence thesis by Def6;
end;
